A "production of tapered bent tube", particularly to a production of tapered bent tube with a consistent thickness and tapering.
Conventionally, a brass musical instrument with a bent tube of different calibers, such as Saxophone, Bass Clarinet, etc., has a bent tube portion, one end of said bent tube portion has a larger caliber while the other end has a smaller caliber; because of the special shapes of tapered bent tubes, in a conventional production, two brass plates are respectively punched and pressed to form the shape of two matching semi-taper bent tubes (a), (a'), then the two semi-taper bent tubes (a), (a') are combined, then its seam is welded to form, as shown in FIG. 6, and since the two components are assembled, there will be two welded seams on its outside, and though the welded seams can be eliminated in a polishing process, the trace will show, so its outside appearance will look coarse and unrefined, which will affect its integred appearance; but the final objective of a musical instrument is perfect sound effect, then the sound effect produced from the tapered bent tube that is composed of two halves of tapered bent tubes a,a' will be unsatisfactory.
Or, a single sheet of brass plate may be rolled to become a tapered tube, then it is bent to become a bent shape, then it is placed inside a mold hole with a tapered bent tube, then it is expanded to form by hydraulic approach; during the bending process of the straight tapered tube, there will be wrinkled folds at the bend, though the wrinkled folds may be eliminated in the expansion process, all the wrinkled folds cannot be eliminated, therefore, its outside appearance looks primitive.
During the expansion process, the expansion ratio on the outside of the tapered bent tube will be larger than that on the inside, as a result, the wall thickness on the outside will be thicker than that on the inside of the tapered bent tube, as a result, the wall thickness of the tapered bent tube will be inconsistent; there will be cracks due to the excessively high expansion ratio on the outside of the tapered bent tube, the final product will be defective; sound is produced from resonance of air flow in the tube of a brass musical instrument, but the resonance will be inconsistent because the thickness on the wall of a tapered bent tube is inconsistent, there will be mutual interference and subsequent noises to affect its sound quality.
Because the inconsistent wall thickness of a conventional product will affect the sound quality of the brass musical instrument, the inventor has devoted in the research and has designed a way of production for tapered bent tube with consistent thickness, whereby a primary mold is used to punch a brass plate to form a U-cup with a full opening, the two ends of the full opening of said U-cup being different calibers, the U-cup is then subjected to tempering treatment to eliminate its processing stress; then, an assembly forming mold is used to punch the full opening of the U-cup to form a rough shape of tapered bent tube with two ends of different calibers, and between the two different calibers is the formation of a flattened part; then, the flattened part on the rough shape of tapered bent tube is removed to form a tapered bent tube; the seam on the tapered bent tube is welded and smoothed by rolling, to complete the two ends with different calibers; in said production, the primary mold forms the outside portion of the tapered bent tube by expansion, then the assembly forming mold forms the inside portion of tapered bent tube by the same expansion approach, therefore, the inside and outside of the tapered bent tube will have approximated expansion ratios, to avoid the occurrence of cracks, to produce a tapered bent tube with a consistent thickness, and to obtain a better sound quality.